I'm professional photographer who is using Canon 6d for 2 years already, over 100 thousand shots. It is fantastic camera but now it is in the end of its production term, and I think Canon will release 6D mark II next year. If so, here is list of desired upgrades, ie what I think 6d mark II should look like:
1. Articulating/Tilting screen. It is very handy feature allowing to use live view mode for precise non center focusing, no need to lie on the floor, you can shoot concerts, events inside crowd of people simply by holding camera in raised hands, yes it is required for pro shooting as well as for enthusiasts.
2. 7 frames per second shooting. 2nd big limitation of current 6d, low frames per second is bad, especially when competitors have 15 fps.
3. Built in Intervalometer. Cheap software realization, but it is very handy to have it built-in, for timelapses and astrophoto, rather then using external device.
4. Focus Peaking. Extremely useful feature, even with autofocus lenses. It allows not only to focus precisely but also teaches photo and videographers how to use their glass precisely, showing real depth of field.
5. Easier WiFi initial setup. I've no problems with it, but several of my friends had troubles and were unable to setup wifi on 6d due to its complexity. Less options per screen and step-by-step automated wizard with in camera help showing how to setup mobile phone or tablet will be fine.
6. 22-24 megapixel matrix with little wider dynamic range, +0.5 ev is fine (just to kick Nikon's ass:)).
I've just found best solution for replacement of articulating screen. It is USB host OTG cable or Wifi + your smartphone or tablet + phone on camera holder + EOS Remote / dslr controller application. Ie you simply use your smartpfone as live view sceen monitor, phone is placed in a holder on the camera.
This solution is more portable (since your phone is always with you), screen quality is better and it is touch sensitive, and what is most important, it weights only ~ 0.2kg, while external hdmi monitor weight is 0.4 kg minimum (excluding heavy battery).
PS: But I still think that built-in articualting screen is a "must have" feature in all new cameras, even used by pros.
I like what you desire in the 6D Mark II, there is one thing that matters to me most in that camera, a viewfinder with 100% coverage.
It's something I enjoy now in my Canon 7D, and Canon should have put viewfinder 100% coverage in the 6D when the Nikon D600 has that.
Which I plan on either the 6D or 6D Mark II, which ever I buy would be my first full frame.
I want a full frame for landscapes and general purpose photography, especially full and partial people pics, cars, off road trucks and buildings.
We all know on full frame we get more light for given camera settings than crop, giving us more control over optical quality, which is what I want.